HCCI is a known process for fueling a diesel engine in a manner that creates a substantially homogeneous air-fuel charge inside an engine cylinder during a compression upstroke of an engine cycle. After a desired quantity of fuel for the charge has been injected into the cylinder to create a substantially homogeneous air-fuel mixture, the increasing compression of the charge by the upstroking piston creates sufficiently large pressure to cause auto-ignition of the charge. In other words, the HCCI mode of operation of a diesel engine may be said to comprise 1) injecting a desired amount of fuel into a cylinder at an appropriate time during the compression upstroke so that the injected fuel mixes with charge air that has entered the cylinder during the preceding intake downstroke and early portion of the compression upstroke in a manner that forms a substantially homogeneous mixture within the cylinder, and then 2) increasingly compressing the mixture to the point of auto-ignition near or at top dead center (TDC). Auto-ignition may occur as the substantially simultaneous spontaneous combustion of vaporized fuel at various locations within the mixture. No additional fuel is injected after auto-ignition.
One of the attributes of HCCI is that relatively lean, or dilute, mixtures can be combusted, keeping the combustion temperatures relatively low. By avoiding the creation of relatively higher combustion temperatures, HCCI can yield significant reductions in the generation of NOx, an undesired constituent of engine exhaust gas.
Another attribute of HCCI is that auto-ignition of a substantially homogeneous air-fuel charge generates more complete combustion and consequently relatively less soot in engine exhaust.
The potential benefit of HCCI on reducing tailpipe emissions is therefore rather significant, and consequently HCCI is a subject of active investigation and development by many scientists and engineers in the engine research and design community.
One aspect of HCCI seems to impose a limit on the extent to which it can provide drastically reduced tailpipe emissions of soot and NOx. At higher engine speeds and larger engine loads, the rate of combustion is difficult to control. Consequently, known engine control strategies may utilize HCCI only at relatively lower speeds and smaller engine loads. At higher speeds and/or larger loads, the engine is fueled so that the fuel combusts by conventional diesel (CD) combustion upon being injected into charge air that has been compressed within a cylinder to a pressure that is sufficiently great to cause the fuel to combust as it is being injected.
With the advent of processor-controlled fuel injection systems capable of controlling fuel injection with precision that allows fuel to be injected at different injection pressures, at different times, and for different durations during an engine cycle over the full range of engine operation, a diesel engine becomes capable of both CD combustion and HCCI combustion.
As will be explained by later description, the present invention takes advantage of the capabilities of those fuel injection and processing systems to control fuel injections in different ways depending on certain aspects of engine operation. Exactly how any particular fuel injection system will be controlled by an associated processing system in any given engine will depend on specifics of the engine, the fuel injection system, and the processing system.
Because a diesel engine that powers a motor vehicle runs at different speeds and loads depending on various inputs to the vehicle and engine that influence engine operation, fueling requirements change as speed and load change. An associated processing system processes data indicative of parameters such as engine speed and engine load to develop control data for setting desired engine fueling for particular operating conditions that will assure proper control of the fuel injection system for various combinations of engine speed and engine load.
U.S. patent application Ser. No. 10/809,254, filed 25 Mar. 2004, discloses a diesel engine and associated processor-controlled fuel injection system that processes certain data to select one of plural fueling modes for operating the engine. When a result of the processing selects a first fueling mode (HCCI mode), the engine is fueled during an engine cycle to create a substantially homogeneous air-fuel charge within one or more combustion chambers. That charge is compressed to combust by auto-ignition, with no more fuel being introduced after auto-ignition. When a result of the processing selects a second fueling mode (HCCI−CD mode), the engine is fueled during an engine cycle to create a substantially homogeneous air-fuel charge within the one or more combustion chambers. That charge is compressed to combust by auto-ignition (HCCI), after which more fuel is introduced into the one or more combustion chambers to provide additional combustion (CD). That engine utilizes HCCI combustion at relatively smaller loads and relatively smaller speeds and what is referred to as HCCI−CD combustion at relatively larger loads and relatively larger speeds.